1. Field of the Invention
This invention relates to the field of video image processing. More particularly, this invention relates to detecting scene changes within a sequence of images.
2. Description of the Prior Art
There are a variety of reasons for which one may wish to detect scene changes. An example is to generate markers within a video image library. In reality the only truly definitive scene change detection is found by the perception of a user identifying changes in the scene activity, such as subject or context changes, and marking these points. However, such a perceptual technique is not realistic for machine implementation which requires a non-perceptual basis.
FIG. 1 of the accompanying drawings illustrates adjacent image fields in differing circumstances. If the pixel values in respective corresponding positions in the two fields are subtracted from one another, then an error signal field is produced. As shown in the top pair of fields of FIG. 1, when the fields are identical, the error signal field is zero throughout. Between the middle pair of fields a scene change has occurred. In this case, the error signal field is significantly non-zero throughout a large portion. In the bottom pair of fields, the scene is the same, but considerable motion has occurred. In this case, a simple subtraction of the respective pixel values within the fields yields an error signal field with sizable non-zero areas.
In order to overcome the problem of detecting scene changes in images with considerable motion, as illustrated by the bottom two fields in FIG. 1, it is possible to use motion compensation techniques. FIG. 2 of the accompanying drawings illustrates such a technique. Motion compensated video signal processing is known (for example see British published patent application GB-A-2263602). When the motion between adjacent fields has been identified, then the later of the fields may be back projected to the time of the earlier of the fields and then the pixel values subtracted to produce an error signal that is compensated for the motion.
A problem with this technique is that a disadvantageously large amount of processing capacity is required by such motion compensated video processing systems making them complex and expensive. An object of the invention is to address this problem.